1. Field of the Invention
The present invention relates to a surface acoustic wave (hereinafter "SAW") signal processor, and more particularly to a SAW signal processor comprising piezoelectric insulator FETs (PI-FETs) taps.
2. Background of the Invention
Previously, SAW devices have been fabricated on Si, GaAs and piezoelectric substrates. With piezoeletric substrates, associated circuits cannot be integrated in a monolithic form. For surface acoustic waves, the piezoelectric properties of the GaAs substrates are relatively small; thus, limiting the bandwidth obtainable with each device. Previously, ZnO has been used to improve the bandwidth of SAW devices fabricated on Si and GaAs. However, it is very difficult to fabricate metal insulator semiconductor (MIS) devices in GaAs together with SAWs, because the interface between the piezoelectric dielectric layer and the GaAs substrate degrades the operating characteristics of the MIS devices.
It is difficult to obtain a close acoustical match between Si substrates and a ZnO piezoelectric dielectric layer. As a result, in ZnO SAW devices fabricated on Si substrates the acoustic waves tend to disperse throughout the device structure; thus, degrading the operation of the SAW devices.